act 5 scene 4 it was assumed that whose heart were elsewhere?

Malcolm says that all Macbeth's soldiers have left him. Their heart is not with Macbeth. The men who still serve him do not love him, they do only what they are ordered to.

Tis his main hope:
For, where there is advantage to be given,
Both more and less have given him the revolt,
And none serve with him but constrainèd things
Whose hearts are absent too.